1. Technical Field
The present invention relates to an apparatus and a method for powder coating, which provide a uniform and strong coating film without any unevenness on works of complex configuration such as tube fitting of iron material, and a powder coat-applying apparatus for carrying out the same. The present invention relates more particularly to an apparatus and a method for powder coating, which enhance the adhesion property of the coating film with respect to the works, thus improving the efficiency of coating operation by eliminating the degreasing step, and for improving the productivity thereof.
2. Description of the Prior Art
In the coat-applying process of the prior art, after a degreasing step for removing the contaminant such as grease adhered on the surface of the works to be coated is effected, a cleaning step, a drip out step, and a drying step are also carried out. Then a coat-applying step, a drying and baking process by irradiating the extreme infrared ray, and cooling step are carried out.
However, when the works of complex configuration are to be dried and baked by irradiating the extreme infrared ray, the surface of the coating is tend to be baked excessively and the adhering surface of the coating is tend to be baked short of the need so that the uneven coating may be formed. Further, the drying and baking process by irradiating the extreme infrared ray is time-consuming process. If it is intended to dry uniformly by irradiating the extreme infrared ray, the coat-applying device will inevitably be enlarged, so that the space and the cost required for establishing the apparatus are also increased substantially.
Further, in the above-mentioned method for coating, the degreasing process must be made before coating the works. Since in the case that the heat is adapted to be provided by irradiating the extreme infrared ray from the outside of the works, the contaminant such as grease interposed between the work and the coating will bring the short of adherence or the separation between the works and the coating film. It is thus reasonable to make degreasing operation on all works respectively. However, the degreasing operation is very cumbersome and is an obstacle to the increased efficiency of the coating process.
A hanger on which a plurality of the works is hanged is employed in the coating operation. During the repeatedly effected coating operations, the coating material scattered around the hanger is adhered thereon, and strongly adhered thereon through the effect of heating operation. It has therefore been necessary to make an extra operation to peel off the adhered coating material from the hanger.
Accordingly the object of the present invention is to eliminate the difficulties involved in the prior art and provide a novel and useful relatively compact coat-applying apparatus for forming a uniform and strong coating film without any unevenness in more efficient manner, and the methods for effecting the same.
These and other objects may be achieved by the apparatus and the method in accordance with the invention as defined in claims.
In accordance with a first embodiment of this invention, provided is an apparatus for powder coating of high frequency induction heating type comprising a coat-applying station for applying a powder coating on a surface of a work to be coated, and a heating station for baking the powder coating by heating the work covered with the powder coating through the high frequency induction heating.
In accordance with a second embodiment of this invention, the coat-applying apparatus is further provided with a hanger for hooking the work, and wherein the hanger is made of a material to which no influence of the high frequency wave can be incurred.
In accordance with a third embodiment of this invention, the apparatus further includes a carrier for displacing the works on a circular horizontal transferring track.
In accordance with a fourth embodiment of this invention, provided is a method for powder coating under the influence of high frequency induction heating including the process steps of a coat-applying process for applying the powder coating on a surface of the work to be coated, and a heating process for baking the powder coating from the interface with each work by heating the work covered with the powder coating through the high frequency induction heating.
In accordance with a fifth embodiment of this invention, the apparatus of the high frequency induction heating type comprises a plurality of process stations including a coat-applying station for applying the powder coating on the work to be coated, and a heating station for baking the powder coating by heating the work covered with the powder coating through the high frequency induction heating, a hanger including hook-mounting bars on which hooks are mounted and a hanger-transfer means for transferring the hanger sequentially to each of the plurality of process stations, wherein the hook includes a mounting-member bended in an inverted xe2x80x9cUxe2x80x9d shape and an arm extending from one end of the mounting-member, and the hook-mounting bar is provided with a plurality of vertically extending recesses spaced apart in the longitudinal direction of the member for removably engaging the mounting-member of the hook.
In the coat-applying device of the structure as mentioned above, the hook can be connected to the hook-mounting bar by mounting the mounting-member of the hook on the bar at any selected vertically extending recess. Thus the hook can be held stably through the engagement of the mounting-member with the recess. The hook can also be removed easily by pulling the mounting-member from the recess.
Thus the hook can be mounted on or removed from the hook-mounting bar only by one action. In this connection, the hook mounted on the hook-mounting bar may be exchanged quickly with another kind of hook in accordance with the shape or the size of the work to be coated. The number of the hooks to be mounted on the bar can be changed easily in accordance with the shape or the size of the work to be coated. The spacing between the hooks can be varied easily in accordance with the shape or the size of the work to be coated. Further, such operation can be effected for adjusting the distance between works and the high frequency induction coils.
The hooks for works are preferably made from a material on which the powder coating is not adhered such as a wire of phosphor bronze. If the mounting-member is formed as a clip configuration, the hook may further be held stably on the hook-mounting bar.
In accordance with a sixth embodiment of this invention, the mounting-member and the arm of the hook are formed from a wire of circular cross section, the top end of the arm extends downwardly from the mounting-member, and a hook portion of an arrow head shape for hanging the work is secured on the top end of the arm. In this connection, the interference due to the foot print of the hook on the flow of injected coating material can be inhibited by making the height of the hook longer than the dimension of the work measured from the hook hole to the upper end thereof, i.e. by positioning the work entirely below the hook-mounting bar. The interference can further be inhibited by making the mounting-member and the arm of the hook from a thin wire. Thus, the problem of uneven coating can be eliminated.
In accordance with a seventh embodiment of this invention, the apparatus includes a plurality of process stations including a coat-applying station for applying the powder coating on the work to be coated, and a heating station for baking the powder coating by heating the work, which has been covered with the powder coating, through the high frequency induction heating, a hanger including hook-mounting bars on which hooks are mounted, and a hanger-transfer means for transferring the hanger sequentially to each of the plurality of process stations, wherein, a pair of high frequency induction coils are arranged in the heating station opposite to each other with disposing the hanger-transferring passage therebetween.
Thus it is unnecessary to form a bending portion on the coil so that the intensity of the inducing effect may hardly be varied, and all works positioned opposite to the coils can be heated uniformly.
In the practice of the present invention, the two coils may be separated in their circuit. However, the means for supplying electric energy to these coils can be simplified by connecting both circuits to unify the circuits with a wire material in which no eddy current would be induced.
In accordance with an eighth embodiment of this invention, the pair of high frequency induction coils are supported on coil supporting bases respectively, the bases can be displaced in opposite directions so that the spacing defined between the coil cases can be enlarged of narrowed, and a coil position control means for controlling the displacement of the coil supporting bases is provided.
In such an arrangement, the distance between coils and the distance between each coil and the works can be adjusted, so that the distance between coils can be enlarged upon transferring the hanger into the heating station, and then the coils can be displaced to the position optimum in the heating operation. In this connection, a variety of sizes of the works can be processed, and the heating condition can be varied in accordance with the kind of the works.
In accordance with a ninth embodiment of this invention, the apparatus includes a tag for storing a position control data of the pair of high frequency induction coils or a representative data thereof, adapted to be mounted on the hanger, a data reading circuit for reading the data stored in the tag, a processor generating a control signal on the basis of the data read through the data reading circuit, and a control circuit for controlling the position of the coils on the basis of the control signal.
Thus, in accordance with the invention, the position of the coils relative to the works i.e. the condition to be controlled for realizing the optimum heating with respect to the kind of the works or the property of the coating material can be adjusted automatically in accordance with the control data or the representative data stored preliminary in the tag.
In accordance with a tenth embodiment of this invention, the apparatus further includes a plurality of process stations including a coat-applying station for applying the powder coating on the work to be coated, and a heating station for baking the powder coating by heating the work covered with the powder coating through the high frequency induction heating, a hanger including a plurality of hooks mounted thereon in the vertical direction, a hanger-transferring means for transferring the hanger into the plurality of process stations sequentially, a tag storing a control data or a representative data thereof adapted to be mounted on the hanger, a data reading circuit for reading the data stored in the tag, a processor generating on the basis of the data read through the data reading circuit a control signal with respect to at least one of the following items to be controlled such as the number of the shifting operation of the spray gun, the amount of the coating to be injected from the spray gun, and the time for heating by means of the high frequency induction coils, and a control circuit for controlling on the basis of the control signal the above mentioned items to be controlled.
In accordance with the invention, the apparatus can be adjusted automatically in accordance with the control data or the representative data stored preliminary in the tag is at least one of the number of the displacement of the spray gun, the amount of the coating material to be applied, and the time for heating by means of the high frequency induction coils i.e. at least one of the conditions to be controlled for realizing the optimum coating application or the optimum heating with respect to the kind of the works or the property of the coating material.
As can be seen from the above, in the invention, one or a plurality of the conditions to be influenced on the coat-applying operation or the quality of the baked coating can be controlled automatically and in optimum with respect to the kind of the works and the coating material. Thus, the inefficient operation, such as stopping the line and/or adjusting the position of the coils required conventionally for changing the condition to be controlled upon varying the kind of the works can be eliminated.
In accordance with the present invention, the coat-applying operation of the hangers can be done under the optimum process condition in accordance with their own control data and the representative data, so that even the hangers of smaller lot can be processed in optimum.
The method for storing data to be adopted in the invention can either be the method for storing the control data in the tag, or the method for storing the concrete control data of each work in the data file and storing only the representative data such as the number identifying the work in the tag. Provided that the SID-TAG SYSTEM is intended to be used, the latter method may be adopted.